For example, in order to determine an operating point used for controlling the fuel battery, a current-voltage characteristic or a current-power characteristic is used as an output characteristic of a fuel battery. The former is a so-called I-V characteristic while the latter is a so-called I-P characteristic. The output characteristic of the fuel battery, which can vary depending on working conditions of the fuel battery, is updated while performing a learning process through actual measurement from moment to moment.
For example, Patent Publication 1 describes a learning process performed on an I-V characteristic used in power source control processing of a fuel battery to compensate for the I-V characteristic in accordance with an operating state of the fuel battery. In this publication, it is determined whether or not a fuel battery system is in steady operation. Then, because an update of the I-V characteristic is regarded as being not applicable while the fuel battery system is not in the steady operation, the power source control processing is performed based on a presently stored I-V characteristic. On the other hand, when the fuel battery system is determined to be in the steady operation, the process is advanced to processing for updating the I-V characteristic. The publication further discloses that, in the processing for updating the I-V characteristic, it is determined whether or not a current value output from the fuel battery at the present time matches a value defined for each predetermined step set in advance. When matching is not determined, the power source control processing is performed based on the presently stored I-V characteristic, and when the matching is determined, the I-V characteristic is updated on the basis of an actual voltage value from a voltage sensor.
In addition, it is also described as a second embodiment that means for calculating an alternating current impedance of the fuel battery is provided, to obtain a theoretical I-V characteristic in which a voltage drop due to an internal resistance corresponding to the alternating current impedance is eliminated. Also for the theoretical I-V characteristic, it is described that an update of the theoretical I-V characteristic is performed during the steady operation when the current value matches the value defined for each predetermined step.
Patent Document 1: JP 2007-48628 A1